A major challenge facing global tuberculosis (TB) eradication efforts is the fact that two billion people are latently infected with Mycobacterium tuberculosis (Mtb), many of whom, especially in the setting of HIV co-infection, will develop reactivation disease. Efforts to gain insight into the molecular mechanisms by which Mtb persists in the host have been impeded by the lack of adequate research models and molecular tools. Current research has focused on identifying individual Mtb genes or host factors required for TB latency and reactivation in specific models and inferring their relevance for TB latency and reactivation in humans. The central hypothesis of this proposal is that no single host or microbial pathway is responsible for Mtb entry into or emergence from latency, but rather, that these complex phenomena are attributable to multiple interdependent host and mycobacterial molecular networks, which cannot be deduced from any one particular model. Using a systems biology approach, including several novel animal models of latent TB infection in combination with transcriptional, proteomic, genetic, imaging, and computational techniques, followed by experimental verification of the data using human samples, we will identify host cytokine networks responsible for immunological control of Mtb growth, as well as Mtb regulatory and metabolic pathways required for bacillary growth restriction and reactivation. Our data are expected to yield: 1) Novel potential drug targets for nonreplicating bacilli, with the goal of shortening the duration of TB chemotherapy; 2) Novel diagnostic markers specific to the latent stage of infection and to reactivation disease; and 3) Novel attenuated vaccine candidates with an inability to reactivate, which would be particularly important in the setting of HIV/AIDS.